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setInterval calling function with an undefined parameter

This question has been flagged as already answered with a link provided above. However, I already read that answer and it only answered how to use setInterval in a for loop. There were no functions being called with parameters passed to them in that solution, and that is my situation, so I couldn't use it to fix my situation.
I'm fairly new to programming, so I'll try to describe as best as I can. In setInterval, I am passing a parameter to the function toggleClusters which setInterval calls. The debugger shows the parameter as being correct. It is a reference to an array position that holds an object literal that contains map marker objects. I seem to be misunderstanding something about what values stay around and what do not when using setInterval, because the debugger shows the correct object literal being passed as an arg, but when the function is called, the debugger shows the obj that is supposed to be passed as undefined. Is it that this passed value no longer exists when the function is called?
function setClusterAnimations() {
for (var i = 0; i < clusters.length; i++) {
//intervalNames stores handle references for stopping any setInterval instances created
intervalNames.push(setInterval(function () {
//clusters[i] will hold an object literal containing marker objects
toggleClusters(clusters[i]);
}, 1000));
}
}
//cObj is coming back as undefined in debugger and bombing
function toggleClusters(cObj) {
var propCount = Object.keys(cObj).length;
for (var prop in cObj){
if (prop.getZIndex() < 200 || prop.getZIndex() == 200 + propCount) {
prop.setZIndex(200);
}
else {
prop.setZindex(prop.getZIndex() + 1)
}
}
}

This is typically the issue with such asynchronous calls as with setInterval(). You can solve this in different ways, one of which is using bind():
for (var i = 0; i < clusters.length; i++) {
//intervalNames stores handle references for stopping any setInterval instances created
intervalNames.push(setInterval(function (i) {
//clusters[i] will hold an object literal containing marker objects
toggleClusters(clusters[i]);
}.bind(null, i), 1000));
}
The toggleClusters(clusters[i]) statement will only be executed when your loop has finished, at which time i will be beyond the correct range (it will be clusters.length). With bind(), and mostly with the function parameter i, you create a separate variable in the scope of the call back function, which gets its value defined at the moment you execute bind(). That i is independent from the original i, and retains the value you have given it via bind().

that is because your "i" variable is not captured in the function passed as an argument to setInverval.
Therefore , when this function is invoked, i is always equal to clusters.length.
consider the differences between the two following pieces of code:
var arr = [1, 2, 3];
var broken = function() {
for(var i = 0; i < arr.length; ++i) {
setInterval(function() {
console.log("broken: " + arr[i]);
}, 1000);
// logs broken: undefined
}
};
var fixed = function() {
for(var i = 0; i < arr.length; ++i) {
setInterval((function(k) {
return function() {
console.log("fixed: " + arr[k]);
}
}(i)), 1000); // i is captured here
}
};

Javascript/jQuery attach different function args to .click() method

What's wrong with this code? Reading this it seems that for each loop the jquery should attach a function with assigned values for each iteration. Instead it's attaching i = 2 to every object. Why is it doing that and how can I get it to attach the expected values (e.g., 0, 1, ...)?
//data.length is 2.
for (i=0; i<data.length; i++) {
// Attach the click function
linkId = 'a#' + pk;
$(linkId).click(function(e) {
e.preventDefault();
console.log(i, pk, data);
});
};
console.log -- each link has the same parameters
2 "52fef25e391a56206f03be6e" [object Array]

You're assuming that a block creates a new variable scope. It doesn't in JavaScript. Only a function execution does.
If you use $.each() instead, the callback you give it will be invoked for each iteration, and so you'll have a new scope for every one.
$.each(data, function(i,item) {
// ^---^---function parameters are local to this scope
// v--declare a variable local to this scope
var linkId = 'a#' + pk;
// v--the function made in this scope can access the local vars
$(linkId).click(function(e) {
e.preventDefault();
console.log(i, pk, data, linkId, data[i]);
});
});

console will be displayed only when you click the $(linkId) but at the time is is already equal to data.length (aka 2 in your case) so it will always display 2

Try to isolate the variable's scope. Declare a var j = i; inside the loop context so it enters the click-callback's scope.

So in order to create a separate scope for each iteration you can also use ordinary closure-functions, and pass current i into it:
for (var i = 0; i < data.length; i++) {
(function(j) {
$('a#' + pk).click(function(e) {
e.preventDefault();
console.log(j, pk, data);
});
})(i);
};

How to pass a variable to a function that's part of the parameters of a function call?

for (var i = 0; i < json.length; i++) {
$.Mustache.load('/mustaches.php', function(i) {
//Do Something
});
}
How do I pass the var i to the function in this case?
EDIT: Sorry I don't actually want to make the Mustache.load call too many times. Only once. How can I do that?

This is a little more complicated than you might think, as you must ensure you pass the right value of i, so that the callback doesn't use the value of end of loop.
for (var i = 0; i < json.length; i++) {
(function(i){
$.Mustache.load('/mustaches.php', function() {
// use i. Call a function if necessary
//Do Something
});
})(i);
}
About the callback term : it refers to a function you pass as argument so that the function you call can call it back.
To understand the code I wrote, you must
understand that the callback is called later, when the loop has finished and so when i in the loop has the value of end of loop
that the scope of a non global variable is the function call in which it is defined. That's why there's this intermediate function : to define another variable i which is called with the value of the loop

An elegant way to solve your question would be using the bind method.
for (var i = 0; i < json.length; i++) {
$.Mustache.load('/mustaches.php', function(i) {
//Do Something
}.bind(this, i));
}
the bind method returns a new function with a new context (in this case this) and applies one (or more) argument(s) to your function (i in this particular case). You can find more about bind and currying here.
EDIT. You can optimise your loop by loading the template only once. In fact, $.Mustache.load fetches /mustache.php on each cycle of the loop. Also, because the function asynchronously fetches the template with AJAX, you might get not consistent ordering in your template (one response may take longer than others). The fix is pretty straightforward: we load the template and then we iterate through the loop.
$.get('/mustache.php').done(function(template){
$.Mustache.add('my-template', template);
for (var i = 0, len = json.length; i < len; ++i) {
var rendered_template = $.Mustache.render('my-template', {
i: i,
...
});
}
});

Wrong Parameter is passed to function

I have the following code that adds an onmouseover event to a bullet onload
for (var i = 0; i <= 3; i++) {
document.getElementById('menu').getElementsByTagName('li')[i].onmouseover = function () { addBarOnHover(i); };
}
This is the function that it is calling. It is supposed to add a css class to the menu item as the mouse goes over it.
function addBarOnHover(node) {
document.getElementById('menu').getElementsByTagName('li')[node].className = "current_page_item"; }
When the function is called, I keep getting the error:
"document.getElementById("menu").getElementsByTagName("li")[node] is
undefined"
The thing that is stumping me is I added an alert(node) statement to the addBarOnHover function to see what the value of the parameter was. The alert said the value of the parameter being passed was 4. I'm not sure how this could happen with the loop I have set up.
Any help would be much appreciated.

This is a common problem when you close over an iteration variable. Wrap the for body in an extra method to capture the value of the iteration variable:
for (var i = 0; i <= 3; i++) {
(function(i){ //here
document.getElementById('menu').getElementsByTagName('li')[i].onmouseover = function () { addBarOnHover(i); };
})(i); //here
}
an anonymous function is created each time the loop is entered, and it is passed the current value of the iteration variable. i inside the anonymous function refers to the argument of this function, rather than the i in the outer scope.
You could also rename the inner variable for clarity:
for(var i=0; i<=3; i++){
(function(ii){
//use ii as i
})(i)
}
Without capturing the iteration variable, the value of i when it is finally used in the anonymous handler has been already changed to 4. There's only one i in the outer scope, shared between all instances of the handler. If you capture the value by an anonymous function, then the argument to that function is used instead.

i is being passed as a reference (not by value), so once the onmouseover callback is called, the value of i has already become 4.
You'll have to create your callback function using another function:
var menu = document.getElementById('menu');
var items = menu.getElementsByTagName('li');
for (var i = 0; i <= 3; i++) {
items[i].onmouseover = (function(i) {
return function() {
addBarOnHover(i);
};
})(i);
}
You could make it a little more readable by making a helper function:
var createCallback = function(i) {
return function() {
addBarOnHover(i);
};
};
for (var i = 0; i <= 3; i++) {
items[i].onmouseover = createCallback(i);
}

How do I execute a function after the callbacks inside a for loop are completed?

I have a for loop in a search function, with a function that does a callback inside the loop, and I want to execute a BUILD() function after the loop, and after all the callbacks are completed. I am not sure how to do that, because the loop finishes before all the callbacks are done. The callbacks are API requests to get me data, and I want to BUILD() with that data.
I read up on deferred, so I tried to put the for loop inside a function to the deferred, and then calling BUILD() on '.then( ... )'. But that doesn't seem to work - I think I am understanding it wrong.
HELP?!
Note, this is using the Google Maps Places API (search and getDetails).
var types = {
'gym' : 'fitness, gym',
'grocery_or_supermarket': ''
}
function search() {
for (var key in types) {
var request = { ... };
service.search(request, searchCallback);
}
// PROBLEM AREA
BUILD();
}
function searchCallback(results, status) {
for (var i = 0; i < results.length; i++) {
var request = { ... };
service.getDetails(request, detailsCallback);
}
}
function detailsCallback(place, status) {
// add place marker to maps and assign info window and info window event
}

With a small modification of your code, it can be achieved.
var total = 1337; // Some number
var internal_counter = 0;
var fn_callback = function() {
searchCallback.apply(this, arguments);
if (++internal_counter === total) {
BUILD();
}
};
for (var i=0; i<total; i++) {
service.search(request, fn_callback);
...
Explanation
First, we create a local function and variable.
The variable is a counter, which is increased when the callback is called.
The function is passed to the asynchronous method (service.search), which calls the original callback. After increasing the counter, check the value of the counter against the variable which holds the total number of iterations. If these are equal, call the finishing function (BUILD).
A complex case: Dealing with nested callbacks.
var types = { '...' : ' ... ' };
function search() {
var keys = Object.keys(types);
var total = keys.length;
// This counter keeps track of the number of completely finished callbacks
// (search_callback has run AND all of its details_callbacks has run)
var internal_counter = 0;
for (var i=0; i<total; i++) {
var request = { '...' : ' ... ' };
services.search(request, fn_searchCallback);
}
// LOCAL Function declaration (which references `internal_counter`)
function fn_searchCallback(results, status) {
// Create a local counter for the callbacks
// I'm showing another way of using a counter: The opposite way
// Instead of counting the # of finished callbacks, count the number
// of *pending* processes. When this counter reaches zero, we're done.
var local_counter = results.length;
for (var i=0; i<results.length; i++) {
service.getDetails(request, fn_detailsCallback);
}
// Another LOCAL function (which references `local_counter`)
function fn_detailsCallback(result, status) {
// Run the function logic of detailsCallback (from the question)
// " ... add place marker to maps and assign info window ... "
// Reduce the counter of pending detailsCallback calls.
// If it's zero, all detailsCallbacks has run.
if (--local_counter === 0) {
// Increase the "completely finished" counter
// and check if we're finished.
if (++internal_counter === total) {
BUILD();
}
}
} // end of fn_detailsCallback
} // end of fn_searchCallback
}
The function logic is explained in the comments. I prefixed the heading of this section with "Complex", because the function makes use of nested local functions and variables. A visual explanation:
var types, BUILD;
function search
var keys, total, internal_counter, fn_searchCallback;
function fn_searchCallback
var result, status; // Declared in the formal arguments
var local_counter, i, fn_detailsCallback;
function fn_detailsCallback
var result, status; // Declared in the formal arguments
In the previous picture, each indention level means a new scope Explanaation on MDN.
When a function is called, say, 42 times, then 42 new local scopes are created, which share the same parent scope. Within a scope, declared variables are not visible to the parent scope. Though variables in the parent scope can be read and updated by variables in the "child" scope, provided that you don't declare a variable with the same name. This feature is used in my answer's function.

I think you understand this already, but as it is the BUILD() is getting called linearly while the previous callback functions are still running. It's like you've created extra threads. One way to solve the problem would be to make BUILD a callback from the search function with the for loop in it. This would guarantee all functionality is complete before calling it.
This question might help implement the callback: Create a custom callback in JavaScript